This research proposes to develop new and more rational approaches to the use of intravenous anesthetics in surgical anesthesia. These concepts will be developed with thiopental, the most commonly used intravenous anesthetic. Presently there are no scientific guidelines for the choice of thiopental induction dose or subsequent maintenance doses when combined with nitrous oxide and intravenous narcotics. Skilled clinicians readily achieve the art of safely using thiopental; however, this may not be the case for trainees or less skilled clinicians who may frequently overdose patients with thiopental, possibly including cardiorespiratory depression and prolonged anesthesia recovery. Pharmacokinetic and pharmacodynamic models will be used to define the relationship between thiopental dose, depth, and duration of anesthesia. Guidelines for the use of thiopental as an induction agent in young and old patients will be developed, along with the decrease of dosage necessary when used concurrently with nitrous oxide and intravenous morphine. From this initial research, it will be possible to develop the concept of continuous infusions of thiopental to maintain surgical anesthesia. The pharmacokinetic and pharmacodynamic models will be used to predict the optimal rapid infusion of thiopental to induce anesthesia, and the subsequent slower infusion rates to maintain anesthesia combined with nitrous oxide and intravenous morphine. This approach will be clinically compared to the current standard of intermittent bolus injections of thiopental based on clinical judgment. An approach to individualizing the maintenance infusion rates, based on the initial response of the patient to the first rapid induction infusion of thiopental, will be developed.